1. Field of the Invention
This invention relates generally to techniques for the presetting of pulse counters and more particularly to an apparatus performing the automatic presetting of a counter to a predetermined initial count without any action on the respective control input terminals of its flip-flops. The invention also relates to an apparatus performing the presetting of a counter to a predetermined initial count, not only without any action on the control input terminals of its flip-flops, but also without the use of its parallel output terminals. At last, the invention relates to an apparatus permitting the display of the state of a counter without using its parallel output terminals.
The apparatus according to the present invention may be used not only for the resetting of counters operating at high frequencies, but also for the presetting of predetermination counters used at very high frequencies as variable-delay circuits.
2. Description of the Prior Art
Usually when it is desired to preset a counter to a given initial count, a pulse is applied to each of the flip-flops of this counter, on its set input (S input) or on its reset input (R input) depending on the desired state. Thus, for example, to preset to nine a 4-digit binary counter, a pulse is applied to the S, R, R and S inputs of the flip-flops having the weights 2.sup.0, 2.sup.1, 2.sup.2 and 2.sup.3 respectively and the flip-flops switch to the states 1, 0, 0, and 1, respectively, which correspond to the binary count nine. Naturally, in the most frequent case where it is required to reset the counter, the pulse is applied to each of the R input of the four flip-flops.
The above-described technique, while suitable at low frequencies, does not work satisfactorily at high frequencies, for example over 100 MHz. This drawback is due to the fact that the input terminals on which the pulses are applied have stray capacitances which lower the cutoff frequency of the counter and thus significantly lower its ability to work satisfactorily at high frequencies.